(1) Field of the Invention
This invention relates a process for separating a specific isomer of dichlorocumene from a mixture containing dichlorocumene isomers.
(2) Description of the Prior Art
Dichlorocumene, in particular, 3,5-dichlorocumene (hereinafter referred to as "3,5-DCC") is important an intermediate substance for agricultural chemicals, medicines and dyes.
Dichlorocumene is obtained by reacting dichlorobenzene with propylene or isopropyl halide in the presence of a catalyst. In particular, 3,5-DCC is obtained by isomerization of 2,4-dichlorocumene (hereinafter referred to as "2,4-DCC") in the presence of the catalyst. 2,4-DCC is obtained by alkylation of m-dichlorobenzene (hereinafter referred to as "m-DCB"). The resulting isomer mixture of dichlorocumene contains mainly 2,4-DCC and 3,5-DCC at thermal equilibrium and further contains unreacted material from m-DCB, a by-product 2,5-dichlorocumene (hereinafter referred to as "2,5-DCC"), and a by product dichlorodiisopropylbenzene (hereinafter referred to as "DCDIPB"), and also contains the catalyst. From the reaction mixture containing dichlorocumene isomers, the catalyst is removed by filtration, and unreacted m-DCB and DCDIPB which high boiling points are removed by distillation. However, considerable difficulties are encountered in separation of a dichlorocumene isomer from the mixture of dichlorocumene isomers by distillation because their boiling points are very close to one another. Therefore, in the past, the mixture of dichlorocumene isomers was alkylated, whereby 2,4-DCC was selectively converted to DCDIPB, and thereafter the 3,5-DCC was separated by distillation (U.S. Pat. No. 4,104,315).
However, since the thus obtained 3,5-DCC still contains a small amount of unreacted 2,4-DCC and by-product 2,5-DCC, the 3,5-DCC is selectively brominated and can be separated and purified by distillation (U.S. Pat. No. 4,087,473).
Recovered unreacted m-DCB and by-product DCDIPB are fed to the prior alkylation process, whereby m-DCB and DCDIPB are converted to 2,4-DCC by transalkylation and reused (U.S. Pat. No. 4,329,524).
However, the prior separation purification process which repeats reactions and distillation such as alkylation (first)--isomerization--removal of catalyst--distillation--alkylation(second)--distillation--bromination--dis tillation is disadvantageous for economical and industrial use.
Moreover, the repetition of the reaction give rise to the increase of undesirable by-product. In the prior art, the problem is retained as both economical disadvantage and low quality of the product.